Ethernet is initially used as a method of connecting and communicating a plurality of computers with each other in an office or a small space, and such a communication network is frequently referred to as a Local Area Network (LAN).
Since the Ethernet generally performs data communications using a shared medium, a Media Access Control (MAC) protocol should be performed, and a CSMA/CD method defined in IEEE 802.3 is used in a wired Ethernet.
Although a 10 Mbps or 100 Mbps class Ethernet is the mainstream in the initial stage, transmission speed thereof has been increased at an incredibly rapid pace in the last several years, and standardization of a 1000 Ethernet beyond gigabit Ethernets has been completed and put into use currently.
In addition, the Ethernet is used even in a transmission area within some tens of kilometers out of an existing office area, and at this point, optical fiber cables are mainly used as a transmission medium. Particularly, the gigabit Ethernet is frequently used as an extremely effective data communication technique in a section which needs a small amount of transmission.
Since transmission through an optical fiber is not a transmission using a shared medium, a Media Access Control technique of a CSMA/CD method is not used. That is, in such a communication network, data are transmitted by only using a frame structure unique to the Ethernet and an Inter Packet gap (IGP).
A representative signal which uses an 8B1013 code is a gigabit Ethernet signal, in which MAC level transmission speed of the gigabit Ethernet is 1 Gbps, and 8B10B is used as a line code for transmission. An 8B10B signal is a signal having a DC-free feature, and it is used together with some control codes to distinguish boundaries of Ethernet MAC frames or as an IDLE pattern and the like. IEEE 802.3 defines twelve types of special codes.
Meanwhile, since a SONET/SDH system mainly for long haul transmission basically defines a digital hierarchy for the sake of voices, it is difficult to accept packet signals of the Ethernet or the like. However, ITU-T has standardized Generic Framing Procedure (GFP) around in the year 2000. A related recommendation is ITU-T G.7041. There are two types of GFPs, and one is GFP-F, which is a method of extracting only Ethernet packets from an Ethernet signal and transferring Ethernet packet information excluding preambles from the packets by mapping the Ethernet packet information to GFP packets as is.
The other one is a GFP-T method, in which an Ethernet signal is processed at the 8B10B code level without extracting the Ethernet packets.
Recently, even a Common Public Radio Interface (CPRI) signal or the like used between a base station and a remote station uses an 8B10B code. Most of Common Public Radio Interface signals are transmitted through an optical fiber cable, and transmission distance thereof is some tens of kilometers in average, and since a large number of optical connectors or the like are used by the nature of network configuration, loss of optical signals is increased, and thus probability of generating a transmission error is increased. Accordingly, in this case, it needs to improve transmission performance by applying a Forward Error Correction (FEC) technique or the like.